Agricultural harvesting machines, such as balers, are used to consolidate and package cut crop material so as to facilitate the storage and handling of the crop material for later use. A baler, such as a large square baler or round baler, picks up the crop material and forms it into bales. On a large square baler, a pickup unit at the front of the baler gathers the cut and windrowed crop material from the ground. The pickup unit includes a pickup roll, and optionally may include other components such as side shields, stub augers, wind guard, etc. A packer unit is used to move the crop material from the pickup unit to a duct or pre-compression chamber. The packer unit forms a wad of crop within the precompression chamber which is then transferred to a bale chamber. For purposes of discussion, the charge of crop material within the pre-compression chamber will be termed a “wad”, and the charge of crop material after being compressed within the main bale chamber will be termed a “flake”. Typically such a packer unit includes packer tines or forks to move the crop material from the pickup unit into the pre-compression chamber. Instead of a packer unit it is also known to use a rotor cutter unit which chops the crop material into smaller pieces. A stuffer unit transfers the wad of crop material in charges from the precompression chamber to the bale chamber. Typically such a stuffer unit includes stuffer forks which are used to move the wad of crop material from the pre-compression chamber to the bale chamber, in sequence with the reciprocating action of a plunger within the bale chamber.
When enough flakes have been added and the bale reaches a full (or other predetermined) size, a yoke with a number of needles is activated to transfer twine through the plunger behind the last compressed flake of the bale to knotters which are actuated to wrap and tie twine, cord or the like around the bale while it is still in the bale chamber. The twine is cut and the formed bale is ejected out the back of the baler as a new bale is formed.
In conventional drive systems the knotters are driven by means of a drive shaft-gearbox combination or by a chain drive. When a knotting cycle is required the knotter assembly is coupled through a one-revolution clutch with the main drive which in turn drives the knotter assembly that is synchronized with the plunger. The needles are connected through a crank mechanism with the knotter shaft and hence are driven in a synchronized manner with the knotters. The first part of the sequence of the knotting cycle is used to bring the needles up towards the knotters where, after a certain degree of rotation of the knotter shaft, the different knotter functions start. This first part of the knotter shaft rotation is also used to bring home some functions of the knotter system that were placed in a park position at the end of the second knot sequence and disengagement of the knotter shaft drive since the needles reached home position.
Drive systems for the knotters and the needles typically include a safety/protection device, mostly a shear bolt or other link to break or slip if the drive system encounters a high resistance. Another problem encountered is related to the timing between the needles and the plunger, which if the needles are not withdrawn from the bale chamber in time the plunger with the new, to be compressed wad, will hit the needles causing damage to the needles.
WO2015/197203 in the name of the applicant addresses at least some of these problems and discloses an agricultural baler with a split drive of the needles and knotters by means of a latch system that controls the needle timing and drive and provides an integral safety mechanism. WO2015197203 discloses an agricultural baler including a bale chamber, a plunger configured to compress crop material in the bale chamber, a counter crank, a plurality of needles, and a pivoting latch system. The counter crank is drivingly coupled to the plunger. The plurality of needles is configured to deliver twine through the bale chamber. The pivoting latch system is drivingly coupled to both the counter crank and the needles. A knotter is activated when the needles reach a predetermined position. The latch system ensures that the needles are always withdrawn from the bale by the same drive that powers the plunger. Although such a system works well, a disadvantage is that the movement of the tucker arms for delivering twine to the knotters is synchronised with the movement of the knotters. Indeed, when there is a problem with a knotter this will result in the tucker arms being stopped with the risk that the needles bump into the tucker arms.